The present invention relates to processes for preparing certain multi-functional metal salt derivatives of heteroatom containing esters, suitable for use in, inter-alia, automatic transmission fluids (ATF).
The metal salt esters which are prepared in accordance with the process of the present invention are derived from esters of hydrocarbyl substituted succinic acid or anhydride and alkanols such as thio alkanols. These materials, as well as various metal salts (e.g., Ni and Zn) thereof are described in U.S. Pat. No. 4,344,853 and British Patent Specification No. 2,085,918. The alkaline earth metal ester salt compounds are described in copending U.S. patent application Ser. No. 763,294, filed Aug. 7, 1985.
The method disclosed in these patents or application for preparing the metal salt ester involves the reaction of the free ester with a metal carboxylate or metal hydroxide in the presence of a suitable solvent such as methanol, water, or tetrahydrofuran. The metal salt ester which is formed precipitates from the reaction mixture and the precipitate is typically collected and washed several times.
A process which involves one or more washing steps is expensive to conduct. Consequently, there has been a continuing search for other processes for preparing such metal salt esters which results in a solubilized product which can be added directly to the formulation into which it is being employed, e.g., without a washing step.
The present invention was developed in response to this search.
The development of alternative processes for synthesizing such solubilized metal salt esters has been complicated by the tendency of these products to gel uncontrollably from solution producing a material essentially unsuitable for the purpose for which it is intended, namely, an additive to power transmitting fluids.
It is this problem of gel formation which the present invention overcomes.
While applicants are not aware of any patents which disclose the presently claimed process, the following patents are mentioned for background purposes.
U.S. Pat. No. 3,933,659 discloses fatty acid esters and amides as friction modifiers for functional fluids; U.S. Pat. No. 4,176,074 describes molybdenum complexes of polyisobutenyl succinic anhydride-amino alkanols as friction modifiers; U.S. Pat. No. 4,105,571 discloses glycerol esters of dimerized fatty acids as friction modifiers in lubricating oils.
Diesters of monohydrohydric alcohols, including those with sulfur linkages, which have been esterified with C.sub.3 -C.sub.24 alkenyl succinic acid are disclosed in U.S. Pat. No. 2,561,232. The diesters disclosed therein are said to be useful as synthetic lubricant fluids. U.S. Pat. Nos. 3,198,737 and 3,278,566 disclose fatty esters having utility as extreme pressure agents. U.S. Pat. No. 2,540,570 discloses glycol esters of rosin or other fatty acids with thioglycols, the compounds being useful as extreme pressure additives.
U.S. Pat. Nos. 3,045,042 and 3,117,091 both disclose partial esters of alkenyl succinic anhydride with a variety of polyhydric alcohols such as 2,2'-thiodiethanol as rust preventive additives in petroleum fractions such as gasoline and other fuels. U.S. Pat. Nos. 3,576,847 and 3,556,997 disclose sulfinyl-containing alkenyl succinates useful as dispersants, corrosion inhibitors and anti-wear agents in lubricating oil and fuel compositions. U.S. Pat. No. 3,381,022 generally discloses esters of C.sub.50 and higher hydrocarbon succinic acids suitable as additives in oils and fuels as well as being suitable plasticizers, detergents and emulsifiers.